The axles of most railway trucks now in use are rigidly constrained, as viewed in plan, to remain parallel in curves as well as on straight track. In view of this, the self-steering properties which are known to exist in and which are inherent in rotating axle wheelsets are prevented from producing a radial axle position in curves, but the wheelsets are not prevented from synchronously oversteering on straight track. In curves, the presence of the resulting large angle of attack between the wheel and the rail causes wear of both the wheel and the rail. The energy dissipated in the wear process causes extra rolling resistance, as well as roughness and attendant noise.
The excess steering motion on straight track can become large enough to cause severe lateral oscillation of the truck parts and the car body at high speed. This lack of steering stability is accompanied by wear of truck parts, loosening of track fastenings, and fatigue failures of car body structure.
The problems of both high-speed stability and curving are effectively solved by truck constructions described in my prior U.S. Pat. No. 4,131,069, issued Dec. 26, 1978, and also in my copending application Ser. No. 948,878, filed Oct. 5, 1978, and have been established by extensive field testing. However, the cost of applying the measures taught by the '069 patent and by application Ser. No. 948,878, may in some cases, restrict this solution to cars in high-mileage service. Accordingly, it would be advantageous to have a less expensive method to reduce the hunting and curving problems of trucks, even if the improved results are not quite as extensive as can be obtained with the constructions shown in the '069 patent, and in said pending application.
It has also been known to use a transverse spring plank in a three-piece freight car truck spanning the two side frames and located between the springs and the side frames. Although these spring planks tend to restrain the parallel yaw motion of the axles and bolster and thereby contribute to high-speed stability, use of such spring planks was generally discontinued in trucks some years ago, in part because the planks were subject to cracking, and in part because the trucks were equipped with plain journal bearings rather than roller bearings; and in such trucks with plain bearings, the stability problem is not severe, in view of which the advantage of using the spring plank is not as great with the plain bearings as it is with roller bearings. However, there is one current roller bearing "premium" truck design, i.e., the National "Swing Motion" truck which uses a spring plank. From field tests of this truck, I have found that, with the roller bearings employed in that truck, the spring plank is a beneficial and low cost way of reducing truck hunting. However, that truck is not in wide use, partly because it is expensive and partly because it does not solve the angle of attack problem in curves.